The southern most range of the Himalayas are the Shivaliks. Shivaliks extend over a width of 10-50 kms and have an altitude varying between 900 and 1100 mts. These ranges are called by different names in different regions: Jammu hills in Jammu region; Mishmi hills in Arunachal Pradesh; Cachar in Assom etc. These parts consist of thick gravel and alluvium. The valleys lying between the Lesser Himalaya and Shivalik ranges are called as Duns. Dehradun, Kotli Dun and Patli Dun are some of the prominent Duns.
The eastern most boundary of the Himalayas is the Brahmaputra valley. In Arunachal Pradesh beyond the Dihang valley, the Himalayas take hair pin bend to the south and act as the eastern boundary of India and run through the north eastern states. These divisions are known as ‘Purvanchal’ and mostly composed of sedimentary sand stones. Regionally, the Purvanchal are known as Patkai hills, the naga hills,manipuri hills,khasi and mizo hills
The formation of the Himalayas influences India’s climate in various ways. These act as barriers protecting the great plains of India from the cold winds of central Asia during severe winter. The Himalayas are the reason for summer rains and monsoon type of climate in regions that are beyond the Western Ghats of India. In its absence, this region would have remained drier. The Himalayan Rivers have a perennial flow since these are fed by the glaciers and bring a lot of silt, making these plains very fertile.